Electromagnetic levitation has been commonly researched for the use in ground transit systems. It is ideal for high-speed applications that require low friction. The principle is simple, use electromagnetic force to balance the force imposed by gravity. However, for attractive levitation the system is unstable and nonlinear. Two dominant approaches to this problem have been to use a state feedback control system or a simple linear PID compensated control architecture. State feedback is a well-known control technique, but is complicated to implement and can rely on linearization of the system dynamics. The simple PID control structure is very easy to implement, but can have severe performance degradation in the presence of noise. This system can usually be identified by its large acoustic noise. This is primarily due to the differential term in the controller. This thesis proposes a solution that uses two concepts: Current Command Generation (CCG) and a closed velocity loop. CCG linearizes the control structure by utilizing the known magnetic properties of the system to convert a desired force to a current for any given air gap. This removes squared command terms from the control structure. This allows for a reliable and predictable implementation of linear feedback control systems. The PID implementation of an attractive levitation system uses two control loops. The inner loop is a current controller, which receives current commands from the outer position loop. The proposed control architecture uses three loops. The innermost loop is the current controller, which receives current commands for the CCG. The middle loop is a velocity controller, which receives commands from the position (outer most) loop and produces force command output used as inputs to the CCG. The three loops consist of two Proportional Integral (PI) controllers for the current and velocity controllers and a Proportional (P) controller. There is no derivative term, making the proposed solution's performance far less dependent on noise. This architecture removes the necessity of nonlinear elements in the control architectures and improves noise rejection through the use of the velocity loop. The acoustic noise performance of this system is enhanced by both of these methodologies and is shown in the experimental setup. / Master of Science

The precise control of spacecraft with flexible appendages is extremely difficult. The complexity of this task is magnified many times when several flexible spacecraft must be controlled precisely and collaboratively, as in formation flying. Formation flying requires a group of spacecraft to fly in a desired trajectory while maintaining both relative positions and velocities with respect to each other. This work enhances two current state-of-the-art formation flying algorithms, specifically leader-follower and virtual-structure architectures. First, a flexible satellite model is integrated into each of these architectures. Second, input shaping is used to generate the satellites desired trajectories, thereby enhancing the performance of the system. This dissertation addresses key issues regarding the application of command generation techniques to flexible satellites controlled with formation flying control architectures. The temporal tracking and the trajectory tracking of each architecture are examined as well as the vibration characteristics of the formation satellites. Design procedures for applying trajectory shaping for the leader-follower and virtual-structure architecture are developed. Experiments performed on a flexible satellite testbed verify key simulated results.

Command generation is a process by which input commands are constructed or modified such that the system's response adheres to a set of desired performance specifications. Previously, a variety of command generation techniques such as input shaping have been used to reduce residual vibration, limit transient deflection, conserve fuel or adhere to numerous other performance specifications or performance measures. This dissertation addresses key issues regarding the application of command generation techniques to tethered satellite systems. The three primary objectives of this research are as follows: 1) create analytically commands that will limit the deflection of flexible systems 2) combine command generation and feedback control to reduce the retrieval time of tethered satellites, and 3) develop command generation techniques for spinning tether systems. More specifically, the proposed research addresses six specific aspects of command generation for tethered satellites systems: 1) create command shapers that can limit the trajectory tracking for a mass under PD control to a pre-specified limit in real time 2) create commands analytically that can limit the transient deflection of a model with one rigid-body and one flexible mode during rest-to-rest maneuvers 3) command generation for a 2-D model of earth-pointing tethered satellites without tether flexibility, 4) command generation for a 2-D model of earth-pointing tethered satellites to reduce tether retrieval time and reduce swing angle, 5) command generation for a 3-D model of earth-pointing tethered satellites without tether flexibility, and 6) command generation for improved spin-up of spinning tethered satellite systems. The proposed research is anticipated to advance the state-of-the-art in the field of command generation for tethered satellite systems and will potentially yield improvements in a number of practical satellite and tether applications.

In this study, universal motion command generator systems utilizing a Field Programmable Gate Array (FPGA) and an interface board for Robotics and Computer Numerical Control (CNC) applications have been developed. These command generation systems can be classified into two main groups as polynomial approximation and data compression based methods. In the former type of command generation methods, the command trajectory is firstly divided into segments according to the inflection points. Then, the segments are approximated using various polynomial techniques. The sequence originating from modeling error can be further included to the generated series. In the second type, higher-order differences of a given trajectory (i.e. position) are computed and the resulting data are compressed via lossless data compression techniques. Besides conventional approaches, a novel compression algorithm is also introduced in the study. This group of methods is capable of generating trajectory data at variable rates in forward and reverse directions. The generation of the commands is carried out according to the feed-rate (i.e. the speed along the trajectory) set by the external logic dynamically. These command generation techniques are implemented in MATLAB and then the best ones from each group are realized using FPGAs and their performances are assessed according to the resources used in the FPGA chip, the speed of command generation, and the memory size in Static Random Access Memory (SRAM) chip located on the development board.

The rapid movement of machines is a challenging control problem because it often results in high levels of vibration. As a result, flexible machines are typically moved relatively slowly to avoid such vibration. Therefore, motion-induced vibration limits the operational speed of the system. Input shaping is one method that eliminates motion-induced vibrations by intelligently designing the reference command such that system vibration is cancelled. It has been successfully implemented on a number of systems, including bridge and tower cranes. The implementation of input shaping on cranes provides a substantial increase in the operational efficiency. Unfortunately, most cranes, once erected, have limited or no base mobility. This limits their workspace. The addition of base mobility could help extend the operational effectiveness of cranes and may also expand crane functionality. Mobile cranes may also be better suited for use in harsh and/or distant environments. Teleoperation of oscillatory systems, such as cranes, then becomes another avenue for advancement of crane functionality. Base mobility in cranes presents both additional control challenges and operational opportunities. A crane with base mobility is redundantly actuated (overactuated), such that multiple combinations of actuators can be used to move a payload from one location to another. This opens the possibility for the selection of a combination of actuation that provides both rapid motion and limited system vibration. The extension of input shaping into this operational domain will provide a method to maximize effective actuation combinations. Toward addressing these issues, new multi-input shaping methods were developed and applied to a mobile, portable tower crane. During this development, a firm understanding of robust input shaping techniques and the compromises inherent to input shaper design was formed. In addition, input shaping was compared to other command generation techniques, namely lowpass and notch filtering, and proven to be superior for vibration reduction in mechanical systems. Another, new class of input shapers was also introduced that limit the input shaper induced overshoot in human operated systems. Finally, a series of crane operator studies investigated the application of input shaping techniques to teleoperated cranes. These studies suggested that input shaping is able to dramatically improve remote crane operator performance.